Molecular analysis using flow cytometry has opened new possibilities for observing the unique phenotypes of single cells. Today, flow cytometry is on the front lines of cancer research and is routinely used to measure gene expression, therapeutic response, DNA content, cycling, drug resistance, and cell-surface markers of single cells. While the advent of this technology has revolutionized cancer research, many important biochemical processes involving small molecules, such as drugs and metabolites, remain invisible to fluorescence probing. Quantitative detection of small molecules with conventional methods (e.g. liquid scintillation counting, mass spectroscopy) is possible, but only in bulk samples for lack of sufficient sensitivity. However, bulk measurements can be misleading because the ensemble average may not accurately represent the individual cell characteristics.
What is needed is a high-throughput single-cell scintillation counting system and method that can sort cells on the basis of the uptake of a small radiolabeled molecule.